A process for production of an arylmercaptan compound is known which comprises reducing an aryl disulfide compound with an iron powder or a zinc powder. This process, however, is troublesome in the disposal of the iron powder or zinc powder used. A process for production of an aryl mercaptan compound from a disulfide compound using an alkali hydroxide, is advantageous in that the process can be carried out under relatively mild reaction conditions. The process, however, has a drawback in that the yield of arylmercaptan compound (an intended product) is low because the product is partially oxidized to generate by-products such as arylsulfinic acid and the like; thus, the process has been unsuitable as an intermediate step for production of an alkoxycarbonylalkylthioaryl compound.
A 2,4-dihalo-5-methoxycarbonylthioaniline derivative obtained from 5,5'-(2,4-dihalogenoaniline) disulfide (which is an aryl disulfide compound above mentioned) represented by the following general formula: ##STR4## is unstable and cannot be isolated at a high yield. Thus, it has been difficult to produce, in industry, an intended alkoxycarbonylalkylthioaryl compound from a substituted aryldisulfide compound which is an expensive raw material.
The task to be achieved by the present invention is to provide industrial processes for producing a metal salt of an arylmercaptan compound and an alkoxycarbonylalkylthioaryl compound in an easy operation at a high yield.
In order to achieve the above task, the present inventors made a study hardly on a process for producing an alkoxycarbonylalkylthioaryl compound. As a result, the present inventors unexpectedly found out that by allowing a sulfur compound to be present in the reaction of an aryl disulfide compound with an alkali metal hydroxide, the aryl disulfide compound can be converted into an alkali metal salt of a corresponding arylmercaptan compound at a high yield, that by reacting said alkali metal salt with a halogenofatty acid ester compound at pH 7-10, said alkali metal salt can be converted into an alkoxycarbonylalkylthioaryl compound easily at a high yield, and that these reactions can be carried out continuously in the same reactor. The present invention has been completed based on the above findings.